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Evolution-enabled application-programming interfaces

Evolution-enabled application-programming interfaces. Ralf L ämmel Data Programmability Team Microsoft, Redmond. Edited for online publication. API asbestos and its remedy. C++ code for window creation in pre-.NET HWND hwndMain = CreateWindowEx( 0, "MainWinClass", "Main Window",

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Evolution-enabled application-programming interfaces

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  1. Evolution-enabled application-programming interfaces Ralf Lämmel Data Programmability Team Microsoft, Redmond Edited for online publication

  2. API asbestos and its remedy C++ code for window creation in pre-.NET HWND hwndMain = CreateWindowEx( 0, "MainWinClass", "Main Window", WS_OVERLAPPEDWINDOW | WS_HSCROLL |WS_VSCROLL, CW_USEDDEFAULT, CW_USEDEFAULT, CW_USEDDEFAULT, CW_USEDEFAULT, (HWND)NULL,(HMENU)NULL,hInstance,NULL); ShowWindow(hwndMain, SW_SHOWDEFAULT); UpdateWindow(hwndMain); .NET version Form form = new Form(); form.Text = "Main Window"; form.Show(); Source of the term “software asbestos”: Klusener, Lämmel, Verhoef: “Architectural modifications to deployed software”, 2005, Science of Computer Programming

  3. Table of contents • Call to arms • More examples • Categorization • Techniques • Show stoppers

  4. Evolutionary API transformationsWhy is that a worthy research challenge? • Improve quality of APIs. • Support effective obsoletion. • Decrease platform complexity. • Orthogonal to model-driven xyz. • Improve productivity of developers.

  5. API evolution samples • CodeDom: program generation • Xml.Schema: XML schema processing • DOM vs. XML binding: API-fication

  6. API asbestos:My first .NET program Sigh! Main.cs(…,…): warning CS0618: 'System.CodeDom.Compiler.CodeDomProvider.CreateGenerator()‘ is obsolete. Use CodeDom API for program generation CodeCompileUnit compileUnit = new CodeCompileUnit(); // ... build some cool code objects CSharpCodeProvider provider = new CSharpCodeProvider(); ICodeGenerator gen = provider.CreateGenerator(); IndentedTextWriter tw = new … // create a text writer gen.GenerateCodeFromCompileUnit(compileUnit, tw, new CodeGeneratorOptions());

  7. Typical developer support

  8. Elimination of the obsolete pattern CodeCompileUnit compileUnit = new CodeCompileUnit(); // ... build some cool code objects CSharpCodeProvider provider = new CSharpCodeProvider(); // ICodeGenerator gen = provider.CreateGenerator(); IndentedTextWriter tw = new … // create a text writer provider.GenerateCodeFromCompileUnit(compileUnit, tw, new CodeGeneratorOptions()); That is, we get rid of the extra generator object, and directly use the Generate… method of the provider object.

  9. How to …? • Find offending “Create” calls. • Get a handle on factory (provider). • Find all uses of created generator. • Setup provider itself as generator. CodeCompileUnit compileUnit = new CodeCompileUnit(); // ... build some cool code objects CSharpCodeProvider provider = new CSharpCodeProvider(); // ICodeGenerator gen = provider.CreateGenerator(); IndentedTextWriter tw = new … // create a text writer provider.GenerateCodeFromCompileUnit(compileUnit, tw, new CodeGeneratorOptions());

  10. More API asbestos:My second .NET program Sigh! Main.cs(…,…): warning CS0618: 'System.Xml.Schema.XmlSchema.Compile(System.Xml. Schema.ValidationEventHandler)' is obsolete: 'Use System.Xml.Schema.XmlSchemaSet for schema compilation and validation.' Use Schema object model (SOM) for schema processing XmlSchema schema = new XmlSchema(); // … do something cool with the schema schema.Compile( new ValidationEventHandler( ValidationCallbackOne));

  11. An attempted modernization XmlSchema schema = new XmlSchema(); // … do something cool with the schema XmlSchemaSet set = new XmlSchemaSet(); set.Add(schema); set.ValidationEventHandler += new ValidationEventHandler( ValidationCallbackOne); // schema.Compile( // new ValidationEventHandler( // ValidationCallbackOne)); set.Compile(); How to get this right? Is the above guess correct anyway?

  12. Deprecated classes, methods, fieldsin Java world Source: Henkel & Diwan: “CatchUp! Capturing and Replaying Refactorings to Support API Evolution” International Conference on Software Engineering, 2005

  13. Burdens implied by API evolution • API producer • Upward compatibility • Extending maintenance • Investments • Tools • Processes • Documentation • API consumer • Re-engineering for eradication • Complexity due to multiple versions

  14. An example for API-fication or translation • Given: a C# program that accesses XML business data through DOM. • Wanted: a converted C# program that uses XML binding instead. • Needed: (This is the naïve version.) • The relevant XML schema(s) • An XML binding technology • A dedicated C# program transformation • Potentially: IDE component

  15. Untyped (DOM-based) XML functionality

  16. Typeful XML functionality

  17. Kinds of API evolution • Refactoring • Service introduction • Service extension • Service elimination • Service restriction • API-fication • API translation • Example: Replacement of DOM by XML binding • Refactoring: Prepare the introduction of XML binding technology • Translation: Replace DOM patterns by schema-derived object model • Extension: Inject additional validation functionality into the application Compare to kinds of grammar adaptation: Lämmel: “Grammar Adaptation”, Formal Methods Europe, 2001

  18. Techniques for API evolution • Weak and strong obsoletion • Provision of facades • Provision of parallel versions • Migration guides, strategies, wizards • Byte-code transformations • Source-code transformations

  19. What about refactoring?

  20. Record refactorings on the API developer’s siteReplay refactorings on the API user’s site Source: Henkel & Diwan: “CatchUp! Capturing and Replaying Refactorings to Support API Evolution” International Conference on Software Engineering, 2005

  21. So what? We cannot expect in general: • a refactoring suite to be sufficiently expressive, • refactoring to be practical for API developer, • a change scenario to be semantics-preserving.

  22. The envisaged transformation framework Musts • Source-code transformation • Source-code model with high fidelity • Type analysis, simple DFA/CFA • Test harness for system under transformation • Simple feedback mechanisms Shoulds • More advanced user interaction • More advanced DFA/CFA/effect analyses • API protocols based on temporal logic • Security models and other constraints • Coverage of multiple (“all”) languages • Story for 80/20 conversions

  23. Potential show stoppers • Language issues • Incompleteness issues • Legal issues

  24. Language issues • Reflection • Threads • Side effects • Third party frameworks • Multitude of languages

  25. Incompleteness issues • API producer can’t convert • API consumer won’t convert

  26. Legal issues • How to sell 80/20 solutions? • Can we promise correctness? • How to prove correctness to client? • Development may rely on client code? • Support may rely on client code?

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